On Wed, Jan 21, 2026 at 04:48:26PM -0800, Thiago Macieira via Std-Proposals wrote:
> On Wednesday, 21 January 2026 14:18:43 Pacific Standard Time Levo D via Std-
> Proposals wrote:
> > Could we fix this somehow?
>
> It isn't broken.

I'm not sure how many developers would say that after looking at the assembly.
 
> GCC is missing some optimisation opportunities there, by emitting the check
> for the initialisation routine's presence repeatedly. Switch to Clang and
> you'll see that it generates much better code. Not that it's perfect: I don't
> understand why it emitted a call to flush(), because the condition should have
> been obvious to be impossible. Maybe it's thinking that the object could
> change between function calls?

I'm not sure how many developers would say that after looking at the assembly.

> > In the link below, someone has written an
> > explanation of the problem. In short, the problem is that we can't see how
> > it's initialized
> > https://discourse.llvm.org/t/whats-with-thread-local-calling-an-initalizer/8
> > 9459/6
>
> Indeed.
>
> >
> > I was thinking about allowing something like `extern MyClass myObj{i,
> > promise, to, init, like, _this_};` However, this may break some behavior.
>
> What behaviour might it break? Because it compiles.

I'm not sure how many developers would say that after looking at the assembly.

> It is even better if you do initialise the array:
> https://godbolt.org/z/xMP1qYqYE

I'm surpised godbolt showed the assembly. If you do that in real code you'll get a redefinition error.

> > Or
> > `[[no_initalizer]] extern MyClass myObj;`
>
> This one semantically makes no sense. It must have an initialiser.
>
> > Or have some kind of rule so it isn't dynamically initialized.
>
> It must be initialised.
>
> > I get into situations where I can't use the gcc __thread attribute, and it
> > occasionally is annoying
> >
> > How should we fix this? It’s a problem in both gcc and clang
>
> There is no problem.

Unless you care about performance, which is why I measured and noticed this years ago.
I was talking to this with a friend (and ran into a situation where __thread won't compile),
I figure this may not get fixed unless asked